Abstract :
The supply transformer neutral is preferably earthed inductively, which means that the network is operated with compensated neutral, in order to reduce fault currents occurring in case of earth faults in electrical distribution networks. The inductance of this arc suppression coil located between the supply transformer neutral and the earth potential is to be readjusted (tuned) to different network configurations after any change in the topology of the network. A newly developed method allows all essential parameters of the zero phase sequence system to be reliably determined, without any adjustment of the arc suppression coil, by feeding non-mains-frequency signals, especially a frequency spectrum, into the zero phase sequence system of the network. This innovative method offers the following advantages: • The degree of detuning, the resonant frequency and the electrical parameters of the zero phase sequence system of the network can be determined exceedingly reliably even in extremely detuned networks. • The method works independently of the amplitude of zero potential. • Supplementary coils in the arc suppression region are identified automatically and are taken into account when the desired degree of compensation is set. • The arc suppression coil itself is only adjusted if tuning is actually required, even under extremely fluctuating network conditions, which results in shorter operating times of the coil drive and thus in increased availability and service life.
